Fig. 3. Yolk sac defects in Tbx3^tm1Pa mutant mice. (A) 12.5 dpc wild-type (+/+) and homozygous Tbx3^tm1Pa mutant (–/–) embryos within the yolk sacs, with the placentas (p) still attached. Vasculature is present in the mutant, but the vessels are smaller. (B-D) PECAM immunostaining on dissected yolk sacs at 10.5 dpc showing extensive endothelial cell organization into vessels in the wild-type (C) yolk sac but a variable degree of endothelial development in the homozygous mutants (B,D). (E,F) Histological sections of yolk sacs from heterozygous and homozygous mutant embryos at 10.5 dpc showing normal development of endoderm and mesoderm layers of the yolk sac, and endothelial cell-lined blood islands or blood vessels. (G,H) Histological sections of yolk sacs from heterozygous and homozygous mutant embryos at 12.5 dpc, showing cell death and degeneration of the endoderm layer and blood islands in the homozygous mutant (H). The endoderm cells in the mutant are pyknotic (arrow); asterisk indicates the remains of a vessel or blood island with degenerating blood cells. There were no obvious differences between +/+ and +/– embryos. en, endoderm; et, endothelium; m, mesoderm; p, placenta.

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